In the Philippine legal landscape, employment contracts are not merely private agreements; they are imbued with public interest. While the Principle of Autonomy allows parties to establish stipulations, clauses, and terms, these are always subject to the overarching police power of the State to protect labor.

The dates specified in an employment contract—specifically the commencement date, probationary milestones, and fixed-term expirations—serve as the structural skeleton of the employer-employee relationship.

1. The Validity of Retroactive Dating

A common query in Philippine labor law is whether a contract can be "backdated" to a period when the employee actually started working.

Fact-Based Commencement: Under the "Four-Fold Test," the employer-employee relationship is established the moment the elements of hiring, payment of wages, power of dismissal, and control are met.
Legal Standing: If an employee started on January 1 but only signed a contract on February 1, the law recognizes January 1 as the true start date. Backdating the contract to January 1 is not only valid but encouraged to ensure accurate computation of benefits like 13th-month pay, service incentive leaves, and SSS/PhilHealth contributions.
Prohibition on "Paper-Only" Dates: Employers cannot use a later date in a contract to circumvent the regularization of an employee who has already rendered actual service.

2. Modification of Dates: Mutual Consent vs. Management Prerogative

Modifying a date in an existing contract (e.g., extending a project duration or moving a start date) requires careful navigation of the Principle of Non-Diminution of Benefits.

A. Mutual Consent

Any significant change to the duration or dates of employment generally requires a Supplemental Agreement or an Addendum. Since a contract is the "law between the parties," one party cannot unilaterally change a date that affects the other's security of tenure.

B. Management Prerogative

Employers have the right to regulate all aspects of employment. However, this prerogative is limited. For example:

Start Date Delays: If an employer moves a start date forward due to operational delays, the employee may be entitled to "standby pay" or damages if they resigned from a previous job based on the original date.
Extension of Probation: This is a high-risk modification. Under Article 281 of the Labor Code, probationary employment shall not exceed six (6) months.

3. The "Six-Month" Rule and Probationary Dates

The date of regularization is often the most litigated date in Philippine labor law.

Strict Timeline: If an employee is allowed to work beyond the probationary date specified in the contract without a valid extension or a termination notice, they become a regular employee by operation of law.
Modification of Probationary Period: The Supreme Court (e.g., in Mariwasa Manufacturing, Inc. vs. Leogardo) has ruled that the 6-month period may be extended only by mutual agreement, usually to give the employee a second chance to meet standards. Without the employee's written consent, any unilateral extension of the date is void.

4. Fixed-Term Employment and "Endo"

Dates are the defining feature of Fixed-Term Employment. For these dates to be valid and not a circumvention of security of tenure, the following must apply:

Certainty: The day certain for the end of the relationship must be specified.
Voluntariness: The employee must have entered into the contract without force, duress, or improper pressure.
Equality: The employer and employee must have dealt with each other on more or less equal terms.

Legal Note: Repeatedly "modifying" or renewing the end date of a fixed-term contract for the same role often leads the Department of Labor and Employment (DOLE) to declare the employee as regular, viewing the dates as a scheme to prevent regularization (Labor Code, Art. 280).

5. Validity of "Floating Status" Dates

In specific industries like security agencies or construction, employees may be placed on "floating status" (temporary off-detail).

The 6-Month Limit: This modification of the work schedule is valid only for a maximum of six (6) months.
Automatic Severance: If the date of "re-assignment" exceeds six months without the employee being given a new post, the law considers the employee constructively dismissed, entitling them to separation pay.

Summary Table: Key Date Considerations

Type of Date	Rule of Validity	Consequence of Improper Modification
Commencement	Must reflect actual first day of work/control.	Underpayment of statutory benefits.
Probationary End	Maximum of 6 months (standard).	Automatic regularization by operation of law.
Fixed-Term End	Must be for a specific project or season.	Deemed regular if used to circumvent tenure.
Floating Status	Maximum of 6 months.	Constructive dismissal after the 6th month.

Conclusion

In the Philippines, the dates in an employment contract are not mere suggestions. The validity of these dates hinges on their alignment with actual service, while their modification requires the meeting of minds and adherence to the Labor Code. Any ambiguity in the dates or their modification is generally interpreted by the courts in favor of labor.